Fresh engine oil is a clear, free-flowing liquid blend of base stock and additives that contains no fuel, water, coolant, dirt, or other contaminants.
When regular engine oil changes are neglected, normally free-flowing lubricating oil breaks down, becomes contaminated, ceases to flow, and is transformed into a thick soup of waste products. That's when serious engine damage is imminent.
Chemistry teaches that engine oil is unstable and decomposes in the presence of oxygen at high temperature. The process, called oxidation, occurs naturally after exposure to normal operating conditions for extended periods of time and is accelerated by exposure to severe operating conditions or to excessively high temperatures. Alternatively, accelerated oxidation may be triggered by a combination of any or all of these factors.
During oxidation, the chemical bonds that define the oil molecules are broken, and some of the reaction products accumulate and interact to form a highly viscous complex mixture of solids, liquids, and gases that contain a variety of solid carbon-based dirt and metallic particles, as well as liquid coolant, fuel, oil and water droplets.
A typical internal combustion engine is just an air compressor in which fuel is mixed with compressed air and then burned. The combustion process generates heat and a variety of reaction products, some of which enter the crankcase as blow-by and contaminate the oil, e.g., fuel, soot, water and other normal reactants, products and by-products.
Even though the oil temperature is high enough to boil off and extract all the water and other volatile contaminants via the PCV system, this crankcase broth will inevitably change into a deposit that does not drain when the oil is changed. Air-cooled gas or diesel engines are just air compressors in which the engine oil is subject to oxidation because they are exposed to higher temperatures and contamination by combustion products. If the engine is liquid-cooled, the engine oil may also become contaminated with coolant.
Sludge formation is not a new problem. In fact, sludge deposits limited the durability of early internal combustion engines. Over the years, oil base stocks were improved, detergent oil additives were developed to keep microscopic sludge-forming solid particles in suspension, anti-oxidation additives were developed to slow the formation of these sludge deposit precursors, and engine oil filters were fitted to remove suspended solid particles from the oil stream and slow the formation of flow restricting sludge deposits on internal surfaces. (Engine Sludge Origins—Don Fedak—Sep. 1, 2001)
Secondly, lubricating compositions also come into contact with seals within the engine in which they are used. Seals are made out of various materials, including nitrile-butadiene rubber (NBR) due to its relatively low cost and high availability, as well as fluorinated elastomers, silicones, and polycarbonates. It is essential that the lubricating composition used has good compatibility with the seals otherwise seals are degraded over time to the point that they fail, leading to fluid leakage increasing maintenance costs, longer down time, and even the risk of engine damage.
Seals deteriorate over time because of heat and age. The stain or film around a push rod tube cover, or weeping around a seam can be eliminated by using certain additives which contain specific components to condition/recondition any seal it touches, keeping it flexible as if new. The result is a much cleaner engine compartment.
Different flexible elastomer seals and gaskets are commonly used in all internal combustion engines of automotive, in particular to prevent contamination and lubricant leakage at those points where moving parts, such as the crankshaft, are in contact with the engine. The main types of these polymer materials are fluoroelastomer, polyacrylates, polysiloxanes and nitrile rubber. The prevention of the deterioration of said seals is very important from the viewpoint of both reliable operation and environmental aspects. There are two primary mechanisms by which seal damage can occur, abrasion due to solid contaminants and the attack of various engine oil compounds. Abrasive damage is not common since most engines have effective lubricant filtration system. The lubricant related damage can occur when some of various lubricant components diffuse into the seals. This will either cause a change in the hardness, thereby leading to swelling and/or elongation, or extract the plasticizer agent used to impart flexibility and strength to polymeric materials.
The unconventional base oils can seriously deteriorate the elastomer seals by extracting their plasticizer compounds causing embrittlement, shrinkage and leakage or penetrating into the elastomer causing swelling. To solve this problem optimal balance of base oils should be applied or so called seal swelling agents (such as dioctyl-sebacate, dihexyl-phthalate, tridecyl-alcohol and organic phosphates, polybutenyl succinic anhydride etc.) have to be used. The elastomer seals can be highly attacked under engine operating conditions by nitrogen containing dispersants, which are used in engine oils in great concentrations (6-10%). These additives contain strongly basic amino groups, which have otherwise high thermal stability and chemical resistance, base-catalyzed elimination occurs, with the consequent formation of unsaturations, and thus the deteriorated elastomer loses elasticity and elongation until it no longer possesses sealing capacity. These problems can easily be occurred due to the presence of low molecular weight succinimides, succinamides and free amines, which can be found in dispersants. Because of their high polarity and small size, these molecules are more likely to diffuse into the seal material and alter its properties. Removal of the free amine and low molecular weight succinimides improves seal performance.
In general, for a given polyisobutenylsuccinimide type dispersant, a higher nitrogen content gives better dispersancy and soot handling but poorer elastomer compatibility. On the other hand, as the operating temperature of the engine rises the rate of the decomposition of the seal rises proportionately.
The balance between soot handling and seal compatibility has provided lubricant formulators with significant challenges over the past ten years, especially as seal testing is a major part of the engine oil approval process around the world. There are numerous ASTM, DIN, ISO, CEC and local standards for investigation of the seal compatibility of engine oils and these can be found in the requirements of performance levels of engine oils.
Reference can be made to Canadian Patent 2523904 which discloses about a novel dispersant having antioxidant properties is obtainable by reacting a succinimide type and/or Mannich type dispersant with a phenolic-substituted ester or acid.
Reference can be made to U.S. Pat. No. 5,925,151 which discloses about a detergent additive composition comprising the combination of a monosuccinimide, derived from polyisobutylene and a polyethylene polyamine, and an aromatic hydrocarbon diluent that may be used in diesel fuel to remove or prevent deposits.
Reference can be made to European Patent 0703959 which discloses about a method of reducing the presence of sludge or varnish precursors in a lubricating oil which comprises contacting a lubricating oil containing sludge or varnish precursors with an oil insoluble, oil wettable cross-linked amine comprising one or more compounds having a dispersant functional group and of an antioxidant functional group.
Reference can be made to European Patent 0310365 which discloses about an invention which provides a lubricating oil dispersant composition, as well as an additive concentrate or lubricant composition incorporating such dispersant, in which the nitrogen-containing moieties of the dispersant compound are compatible with fluorohydrocarbon-containing elastomeric engine seals.
Reference can be made to US Patent Application 20150191673 which discloses about an additive package for a lubricant composition that improves fluoropolymer compatibility of the lubricant composition. The additive package comprises a halide seal compatibility additive and a second seal compatibility additive. The second seal compatibility additive is different from the halide seal compatibility additive. The weight of the second seal compatibility additive in the additive package is greater than or equal to the weight of the halide seal compatibility additive in the additive package.
Reference can be made to European Patent 1354933 which discloses about a lubricating oil composition displaying excellent low temperature valve train wear performance, improved fuel economy retention properties and compatibility with fluoroelastomer-based engine seals.